1. Field of the Invention
The present invention relates to a high-density powdered detergent composition. In particular, it relates to a high-density powdered detergent composition exhibiting high detergency and containing an organic builder excellent in biodegradability.
2. Description of Related Art
A detergent composition for clothes is basically composed of a surfactant which solubilizes soil, separates it from fibers, and dissolves or disperses it in a washing solution, an alkaline substance which accelerates the decomposition or solubilization of soil, a high-molecular compound which suspends soil in a washing solution, a sequestering agent which removes substances lowering the power of surfactants, for example, calcium or magnesium ions from a washing solution, and so on.
Among these components, "builders for detergents" generally refer to substances which do not exhibit detergency per se but can enhance the detergency of a surfactant when used together with the surfactant. Among such builders for detergents, the above-mentioned sequestering agent serves to make a surfactant exhibit its performance more effectively, thus being one of the extremely important builders for detergents.
Phosphate salts such as sodium tripolyphosphate were formerly added to detergents for clothes as the sequestering agent. However, such phosphate salts are believed to be one of the factors causing the eutrophication of lakes, marshes and so on. In the detergent industry, therefore, the development of a detergent not containing any phosphate builder has been continued. As a result, a crystalline sodium aluminosilicate having a specific structure (which is called "zeolite" in the detergent industry) is currently used as the main component of the sequestering agent, because it is free from the above problem unlike phosphate builders and has recently been stabilized in the cost.
Further, a detergent composition for clothes has changed in the form from the late 1980s, so that a so-called compact detergent which has a high bulk density and is lowered in the volume of the composition used per washing run is now widely used. However, the particles constituting such a compact detergent are more highly compacted than those constituting the detergent of the prior art, thus being problematic in solubility. In particular, zeolite which is one of the constituents of the compact detergent is insoluble in water per se, and therefore often causes the generation of water insolubles when washing with the compact detergent. The applicants of the present invention have made attempts to solve this problem by exerting ingenuities in the formulation or production process of the compact detergent. However, such a solution is often accompanied with the restriction of the formulation. Under these circumstances, a better builder for detergents is being developed for the purpose of attaining progression in the industry.
In addition to zeolite, crystalline silicates are also used as builders for detergents. For example, JP-A 60-227895 discloses the use of crystalline silicates as water softeners; JP-A 6-10000, 2-176398 and 7-53992 disclose detergent compositions containing crystalline silicates; and JP-A 5-184946 and 6-116588 disclose specific crystalline silicates and detergent compositions containing them.
As described above, zeolite is a water-insoluble builder for detergents. On the other hand, water-soluble builders for detergents include organic builders such as salts of polycarboxylic acids, and specific examples of such salts include citrates, malates, salts of nitrilotriacetic acid (NTA), salts of ethylenediaminetetraacetic acid (EDTA) and polymers of carboxylated vinyl compounds. The term "polymers of carboxylated vinyl compounds" refers to, e.g., polyacrylate salts, salts of acrylic acid/maleic acid copolymers, and salts of olefin/maleic acid copolymers, whose molecular weights lie within the oligomeric region. However, concern is shown for the use of these organic builders, because the organic builders are disadvantageous in that the sequestering power is unsatisfactory, that the toxicity to fish has been pointed out and/or that the biodegradability is poor.
From the standpoint of the influence on the environment, studies have recently been made on builders excellent in biodegradability and sequestering power. For example, specific organic builders prepared by the reaction of epoxysuccinic acid or maleic acid with aspartic acid and detergent compositions containing them are disclosed in JP-A 5-170714, and this patent document also describes that these builders are excellent in biodegradability and detergency-enhancing effect. Further, JP-A 6-248300 discloses a detergent composition containing an organic builder consisting of hydroxyiminodisuccinic acid salt in a specific amount. Furthermore, it has been reported by BASF that glycine-N,N-diacetic acid derivatives are excellent in biodegradability and sequestering power, and are therefore extremely suitable for builders for detergents (New Horizons' 95 Conference Lake George, New York, Sep. 19-22, 1995). In the detergent composition reported in this conference, a surfactant mixture comprising 9% of FAS (a salt of sulfate ester of higher aliphatic alcohol) and 10% of a nonionic surfactant is used together with a glycine-N,N-diacetic acid derivative, zeolite, soda ash, perboric acid and/or TAED (tetraacetylethylenediamine).
Meanwhile, it is believed that there is a good possibility of further enhancing the detergency of a detergent composition containing a glycine-N,N-diacetic acid derivative as the organic builder. In particular, no optimum formulation has been found as yet with respect to a high-density detergent composition which comprises a surfactant component comprising a nonionic surfactant as the base and a proper amount of an anionic surfactant, and a builder component comprising both the above organic builder and an inorganic builder such as zeolite or crystalline silicate.